Apparatus and methods for analyzing a sample solution are widely used in manufacturing operations. For example, in the manufacture of semiconductor devices, semiconductor wafers are often cleaned using deionized water. It is important to analyze the deionized water to insure that an acceptably low level of ions, including positive ions and negative ions, is present in the deionized water.
FIG. 1 shows a conventional solution analyzing apparatus illustrating a first solution flow channel. As illustrated by the arrows, a sample solution such as a sample semiconductor cleaning solution, contained in a sample vessel 10 is filled through a sample solution supply line 12 into a sample loop line 18 of a positive ion detector "A". The sample solution then continues to be filled through the sample loop line 18 into a sample loop line 28 of a negative ion detector "B".
The positive and negative ion detectors "A" and "B" are serially connected through a solution passing line 22. This line 22 is provided to transfer the sample solution through the sample loop line 18 of the positive ion detector "A" to the other sample loop line 28 of the negative ion detector "B". The sample vessel 10 generally contains a small amount of sample solution, for example, a cleaning solution of semiconductor substrates which is obtained from a main cleaning solution container (not shown).
Referring again to FIG. 1, the sample solution flows through the supply line 12 to the directional valve 14 of the positive ion detector "A". This valve 14 is controlled by a control signal from a controller 1 so that the sample solution can fill up the sample loop line 18. The filled sample solution of the sample loop line 18 passes through a directional valve 20 to the solution passing line 22 under control of the controller 1. The sample solution in the solution passing line 22 flows through a directional valve 24, the sample loop line 28 and a directional valve 30 of the negative ion detector "B" to an outlet line 32. This solution flow channel is formed by the directional valves which are controlled in response to the control signals of the controller to allow the sample solution to be filled into the sample loop lines 18 and 28 of the detectors "A" and "B". This solution flow step is hereinafter called a sample supplying step.
FIG. 2 shows the conventional solution analyzing apparatus illustrating a second solution flow channel in which the filled sample solution is supplied from the sample loop lines 18 and 28 to two conductivity detectors 40 and 48 respectively, one of which is provided to detect a positive ion component contained in the sample solution and the other of which detects a negative ion component contained in the sample solution. This solution flow channel is also formed by means of the directional valves in response to the control signals of the controller 1.
Referring again to FIG. 2, the filled sample solutions in the sample loop lines 18 and 28 flow through the directional valves 14 and 24 to the conductivity detectors 40 and 48, respectively. When pump 34 starts to operate in response to a control signal from the controller 1, a loading solution pumped by the pump 34 can flow through a loading solution supply line 36 to the directional valve 20. Then the sample solution filled in the sample loop line 18 is pushed up out of the sample loop line 18 and is provided to the conductivity detector 40. This solution flow step is hereinafter called a sample loading step. Because the directional valves are controlled in response to the control signals to form the solution supplying channel to the conductivity detector, the sample solution in the sample loop line 18 is supplied through the directional valve 14 to the conductivity detector 40. The conductivity detector 40 analyzes the supplied solution and detects a positive ion component.
Also, when pump 42 starts to operate in response to a control signal from the controller 1, a loading solution, for example, an HCl solution, pumped by the pump 42, can flow through a loading solution supply line 44 to the directional valve 30. The sample solution filled in the sample loop line 28 is pushed up out of the sample loop line 28 and is provided to the conductivity detector 48. Because the directional valves are controlled in response to the control signals to form the solution supplying channel to the conductivity detector, the sample solution in the sample loop line 28 is supplied through the directional valve 24 to the conductivity detector 48. The conductivity detector 48 analyzes the supplied solution and detects a negative ion component.
After detecting the ion components of the sample solution, if the conventional sample solution analyzing apparatus again detects a new sample solution, it is again operated according to the above described method. That is, a new sample solution from the sample vessel 10 is filled into the sample loop lines 18 and 28 through the first solution flow channel, as shown in FIG. 1, and then the filled solutions of the lines 18 and 28 are supplied to the conductivity detectors 40 and 48 through the second solution flow channel, as shown in FIG. 2. However, even though the new sample solution from the vessel 10 flows through the first solution flow channel so as to fill up the first and second sample loop lines 18 and 28 and the previously filled solution (i.e., HCl solution) in the sample loop lines 18 and 28 is dispensed through the outlet line 32, an extremely small amount of the HCl solution may remain in the sample loop line 28 of the negative ion detector "B". Because of the extremely small HCl solution which remains, it may be difficult for the conventional solution analyzing apparatus to accurately detect the ion components of the new sample solution, as shown in FIGS. 3 and 4.
From FIG. 3, it can be seen that, when deionized water is used as a sample solution, a peak value "C" is detected at about 4.2 minutes during the detection of negative ion components contained in the deionized water. Here, the peak value indicates that the deionized water is contaminated with the loading solution, for example, an extremely small HCl solution, remaining in the sample loop line 28.
In addition, when analyzing a component indicating the peak value by high performance ion chromatography, and an MSA (methane sulfonic acid) solution is used as a loading solution and deionized water is used as a sample solution, a large peak value "D" may be found as shown in FIG. 4. This is because the sample loop line 28 of the negative ion detector "B" has been contaminated with the MSA solution.
Accordingly, since negative ion components Cl.sup.- of the HCl solution or positive ion components of MSA may contaminate the sample loop line 28 during the sample loading step, it may be difficult to accurately detect an extremely small ion component contained in the sample solution. Also, even if the sample solution supply line 12 is connected to the ion detector "B", it may be difficult to accurately detect an extremely small ion component contained in the sample solution. This is because ion components of the loading solution may contaminate the sample loop line 18 of the ion detector "A".